What kind of scale for measuring pc inks?

The cost of the scale that you want to buy will be directly proportional to the accuracy required; 1.0 Gram, 0.1 Gram, or 0.01 Gram and the capacity 100 Gram, 1.0 KG, or 4.0 KG. A common scale for people mixing 1 Qt. quantities using Pigment Concentrate is a 1.0 or 1.2KG scale with a 0.01 gram accuracy. This type of scale can cost up to $200. Dropping back to a tenth of a gram accuracy (0.1 gram) and the same 1.2KG capacity scale will run you under $40. If you're going to step up to one gallon mixing you need to look at a 4.0 to 5.0KG scale with an accuracy of 0.1 gram which will run you around $150.

Also, unless you are going to be utilizing different bases with a common pigment system I'd recommend that you look at some of the intermediate / balanced color mixing systems such as the Wilflex Equalizer, or Rutland Color Booster systems. These color matching systems don't require the same high degree of accuracy in mixing and have an inbuilt safety system, in as much as they are manufactured as balanced systems meaning that you cant get out of balance with your pigment to base ratios.